Why is my breakup so much more painful to deal with as it gets later in the day? I always have such an intense urge to call before bed?

I usually can do ok during the day but as it gets later it gets worse and I get more and more sad. I usually have an extremely intense urge to call him before I go to sleep. My brain starts telling me "if you call him tonight maybe you can fix it and he will want you back" which is never the case. But it gets so much worse at night! Why?